The aims of the present work are to manufacture a micro compression tester to measure the mechanical properties of a particle aggregate formed in a shear flow, and to investigate the effect of several factors on the compressive deformation characteristics of the aggregate. This year, the followings were carried out.1.Manufacture of glass fiber probe : a manufacturing technique of a glass fiber probe to compress a particle aggregate was established by combining hydrofluoric acid etching and optical polishing.2.Visualization of compressive deformation behavior of particle aggregate : a three-dimensional visualization technique of aggregate by superimposing laser scanning confocal microscope images was established.3.Compression test : the compression test of a particle aggregate formed in a shear flow was carried out, and the effectiveness of a micro compression tester developed here was demonstrated.Before the compression test, the aggregation and breakup behaviors of latex particles in shear flow confined between two parallel plates were investigated using an in situ observation apparatus with a laser scanning confocal microscope. As a result, the average size of the aggregates decreases as shear rate increases and the gap width decreases due to the hydrodynamic effect acting on the aggregates. The size distributions of the aggregates become narrow as the gap width decreases. In addition, the fractal dimension, i.e., the structure of the aggregates, was almost independent of shear rate and the gap width, and approximately 1.2, which suggests that the aggregates are relatively compact.